1. Field of the Invention
This invention relates to a probe and a system for detecting wear of a refractory wall by the use of the probe.
2. Description of the Prior Art
The bodies of blast furnaces, converters and ladles which constitute a container for holding hot molten metal or for conducting vigorous metallurgical reactions at high temperature, as well as the bodies of soaking pits which internally maintain high temperatures over a long time period, generally have a lining of refractory material on the inner side of a frame or housing formed by a shell or the like. Such a lining layer is repeatedly subjected to thermal and/or mechanical shocks, and as a result it is gradually enbrittled and a worn-out refractory wall easily comes off unless a repair is made. Therefore, from the standpoint of safe operation, it is essential to hold the condition of wear of the refractory material (or the degree of persistence) constantly under strict supervision.
In this connection, the most popular method has been to estimate the condition of the refractory layer from the appearance or temperature of the outer shell, which is of course very low in accuracy. Therefore, the present inventors proposed in their Laid-Open Japanese Utility Specification No. 55-105140 a temperature distribution sensor which is capable of detecting the condition of the inner refractory wall surface with a relatively high accuracy when applied by the refractory wall wear monitoring method disclosed in Laid-Open Japanese Patent Specification No. 55-119114. However, the just-mentioned method which depends on arithmetic operations by a computer is difficult to apply readily to various kinds of refractory walls and thus lacks versatility. Of course, if a sensor which is embedded in a refractory wall is ruptured by wear of the refractory wall, it produces an abnormal output signal which could be used for the detection of the critical condition of the refractory wall in a simple method of wear detection. However, as the afore-mentioned thermal sensor utilizes a sheath type thermocouple or sheath type resistance thermometer, its output signal is essentially a temperature signal. Therefore, it is not always easy to distinguish a signal variation due to a sudden change in the furnace temperature from a variation due to the rupture of the sensor. Consequently, there are possibilities of making a detrimental error in judgement, still leaving a problem with regard to the reliability of operation.
Further, Japanese Utility Model Publication No. 53-8370 discloses a sheath type multi-point temperature probe having plural sheath type thermocouples or plural sheath type resistance thermometers formed by connecting wires of predetermined lengths to the fore ends of heat sensing points and accommodated in a protective tube with the respective heat sensing points located in different positions along the length of the protective tube, the outer diameter of the protective tube being reduced subsequently to form an integral probe assembly. This probe assembly differs from the above-mentioned sensor in that it uses no insulating material between the sheath and protective tube and the material which constitutes the thermocouples of resistance thermometers is not used at the heat sensing points.
Under these circumstances, the present inventors furthered their studies in search for simpler and more reliable means which is capable of accurately detecting the condition of wear of refractory walls, and as a result succeeded in developing a novel probe which will be described hereinlater, and a detection circuit which is suitably used in combination with the probe. This detection circuit differs from ordinary disconnection detecting means which are generally arranged to detect an abnormal state by way of a variation in the resistance across a detecting element which shows different values in shortcircuited and disconnected states. For example, means for detecting an abnormal state of a thermocouple are disclosed in Laid-Open Japanese Patent Application Nos. 55-60828 and 55-117982, Japanese Utility Model Publication No. 55-11456 and Laid-Open Japanese Utility Model Application No. 54-102167. However, if these known detecting means are applied to a molten metal processing system such as blast furnace or converter, the abnormal state is often overlooked as a variation in resistance is very small even in the event of a wire breakage, due to slag deposition at the end of the detecting element, or the molten pig iron or molten steel which contacts the end of the detecting element creates a shortcircuited state despite the presence of a wire breakage, showing only a slight variation in resistance.
In view of these problems, the present inventors endevored to develop a detection circuit which can detect even an instantaneous variation in resistance which may take place by occurrence of an abnormal state, and succeeded in obtaining a novel detection circuit of satisfactory performance characteristics.
In this connection, a mention may be made of DE-OS 2,005,399 disclosing a device for monitoring wear of a refractory layer, which however has to be improved in a number of points before application as a detecting means in an actual operation and lacks practicality. More specifically, this monitoring device has a difficulty in that it requires boring many holes in the refractory wall itself and laying detection wires in the refractory bricks before building the wall, coupled with the problem of reliability arising from the limited number of circuit systems.